IL fiber pathways. A, 3D rendering of IL fiber pathways. To better visualize the fiber bundles, the 3D rendering is presented with the contralateral cortex and ipsilateral striatum after removal of the ipsilateral cortex from a back coronal (top), lateral sagittal (middle), and dorsal horizontal (bottom) view. Note the complexity of IL projections compared with the other cases. The IL–thalamic axons are segregated from the striatal/brainstem axons at the level of the injection site. Fibers bifurcate from the thalamic bundle to travel across the anterior commissure to the internal capsule. B, Schematic illustration of IL bundle subdivisions. C, Photomicrograph showing three segregated bundles within the striatum: a brainstem bundle traveling across the striatum and the internal capsule and a thalamic bundle crossing the ventral striatum from which a third bundle deviates to travel within the anterior commissure to then merge with the main brainstem bundle. Bottom left, Coronal section for orientation. AC-BS, Brainstem fibers passing through the anterior commissure; AP, anterior–posterior distance from bregma; BS, brainstem; Cn, contralateral fibers; Inj, injection site; Str/BS, striatum/brainstem; Th, thalamus.